For annealing, brazing or sintering, furnace atmospheres help ensure that metals thermal processors obtain the results they need. Hydrogen-containing atmospheres are used to protect surfaces from oxidation, and to ensure satisfactory thermal processing results. Hydrogen-containing atmospheres make thermal processing more forgiving because the hydrogen improves heat conduction and actively cleans heated surfaces – reducing oxides and destroying surface impurities. For powder based fabrication such as P/M, MIM or binder-jet metal AM, the use of a hydrogen-containing thermal processing atmosphere ensures the highest possible density of the sintered parts without necessitating the use of post-processing techniques. Users of pure hydrogen or hydrogen-containing gas blend atmospheres often struggle with hydrogen supply options. Hydrogen storage may create compliance problems due to its flammability and high energy content. Hydrogen generation enables hydrogen use without hydrogen storage issues. Deployment of hydrogen generation can ease the addition of thermal processing atmospheres to new and existing processing facilities.

This paper compares and contrasts heat treat processes and equipment typically used to harden gears. It discusses the basic design and operation of vacuum, controlled atmosphere, and hybrid furnaces and process techniques such as carburizing, carbonitriding, nitriding, nitrocarburizing, and neutral hardening. It also includes information on operating and maintenance costs, using batch integral quench furnaces as the base case for comparison. A discussion on when to consider continuous furnace types is included as well.

The atmospheres used in a brazing furnace play a critical role in the final quality and metallurgical properties of the brazed component. Typically, exothermic, dissociated ammonia and nitrogen/hydrogen atmospheres are used for brazing mild steel, alloy steel and stainless steel components. The atmosphere composition, flow rates, pressures, and dew point are some of the key variables control final quality. Almost all brazing companies have quality issues that directly result from improper atmosphere application and control. Common problems include oxidation, flashing, inadequate braze flow, sooting, decarburization and carbon pickup. This troubleshooting presentation reviews years of field experience with nitrogen and hydrogen based atmosphere systems. It will help the heat treater or the brazing production engineer to identify these problems and apply appropriate corrective action.

Studying the gas composition of an atmosphere furnace reveals many parameters that can be used to predict metallurgical results of parts being processed. Today’s heat treaters strive for process consistency in order to eliminate variability, rework, and (in the worst case) scrap. In atmosphere heat treating, understanding control parameters and atmosphere composition provides critical insight into expected results. In this presentation, the audience will have the opportunity to observe gas compositions that would typically be found in carbon-neutral or carbon-rich atmospheres; they will also be able to see how atmospheric properties directly affect the metallurgical properties of heat treated parts. The presenter will illustrate examples of common atmospheres based on furnace types and will discuss common characteristics of improperly controlled atmospheres and how those atmospheres can lead to flawed results. Real-world examples of metallurgical results will be used to illustrate what can be expected from an “out of control” situation.

The potential for improving mechanical properties of steels via thermal processing (e.g. austenization and rapid quenching) through modified phase equilibria in the presence of a high magnetic field has been the subject of numerous recent works [1,2]. In this study, torsional fatigue performance of case-carburized SAE 8620 re-austenitized and quenched inside of a 9 Tesla, 5” diameter superconducting magnet is reviewed. Conventional atmosphere furnace carburized hardened and tempered, and in-situ magnetic field re-hardened and tempered material (Induction Thermo-Magnetic Processing, or “ITMP”) was subjected to fully-reversed torsional loading. Both Special Bar Quality (SBQ) bar and forged SBQ bar steel in carburized conditions were heat treated and mechanically tested. There was no measurable difference in fatigue behavior for either condition when comparing conventionally heat-treated and ITMP re-hardened populations.

In gas carburizing, the source of carbon is a carbon-rich furnace atmosphere produced either from gaseous hydrocarbons or from vaporized hydrocarbon liquids. Using theoretical steps with anticipated process variable inputs allows for the prediction of the carbon available to the steel surface; diffusion can be simulated. Inputs captured during a real-time run can predict the carbon buildup in a part. The simulation and real-time data can be matched up to compare metallurgical results. We will cover principles of atmosphere carburizing, including sensor and control technology. We will discuss the analysis of input variables associated with carburizing applications and understanding the effects the atmosphere, temperature and time have on results. We will look at information using three-gas analysis as opposed to analysis using oxygen probes and review what an atmosphere would look like during a carburizing run. We will review real world scenarios with actual data that allow for a comparison of simulation versus calculated carbon transfer and diffusion against metallurgical lab results.

Furnace atmospheres are critical to meeting metallurgical specifications defined by control processes. The makeup of a furnace's atmosphere in the heat treating process varies based upon the application. This session will cover the different types of atmospheres, the sensors used to measure the atmosphere, and troubleshooting procedures for validation of the environment.

This presentation will discuss a flexible atmosphere heat treating system employing salt quench systems that are considerably faster, than existing technology utilizing internal quench systems. Topics include: improved temperature control, temperature uniformity/uniformity of the austenitizing process; improved automation and reliability of material handling transfers from the austenitizing furnace to the quench system; and increased flexibility, with regard to the quench system, to allow for the widest range of processes to be run in the system.

Austenitic stainless steels are critical in the modern economies with applications ranging from food processing and cryogenic machinery to medical implants and aerospace instrumentation. Tough, resistant to low-temperature embrittlement and many forms of corrosion, these steels are, nevertheless, prone to scratching and galling in service. Case hardening was found to be effective when combined with corrosive surface treatments or in low-pressure, direct plasma-ion discharges, but inhibited in simple atmospheric-pressure furnaces. This paper presents preliminary evaluation of new, rapid (3-4 hrs) nitriding and carbonitriding treatments at low- (500-565°C) and high- (1100°C) temperature ranges involving injection of high-voltage, electric arc-activated, N2-based, NH3 and hydrocarbon gas mixes to the conventional box furnace. Reported data includes characterization of stainless steel product layers using SEM-EDS, XRD, OM, Leco elemental analysis, and microhardness profiling, as well as laser gas analysis of the residual furnace atmosphere.